The present invention relates to combining and mixing substances in fluid form, particularly substances which have differing viscosities and particularly when one substance is an extrudate, particularly a food composition extrudate. The present invention also relates to partitioning a flow of a substance into a plurality of flows and treating the partitioned flows to obtain a plurality of products having differing characteristics, particularly when the substance partitioned has been processed by extrusion techniques and particularly when that substance is an extruded food composition.
As is known, obtaining a substantially homogeneous mixture of substances having differing viscosities is problematic. In particular, the dynamics of the differing viscosities of the substances make it difficult, without intensive mixing, to obtain a uniform distribution of a lower viscosity substance, such as additive substances added in relatively small amounts on the order of, for example, less than about 5%, or even less than 1% by weight, in a higher viscosity substance, since the lower viscosity substance inherently tends to resist combining with the higher viscosity substance. Moreover, intensive mixing is not desirable in many cases, particularly when the higher viscosity substance processed is sensitive to and adversely affected physically, or even compositionally, by effects of mechanical shear. Particularly affected are substances which have been processed by extrusion techniques, such substances including, but not limited to, extrusion-cooked food compositions, for example.
As is known, static mixers, including such as disclosed and referred to in King, U.S. Pat. No. 4,208,136, long have been employed to minimize temperature differentials of a fluid stream and for mixing various products. However, as King subsequently took note, as disclosed in each of King, U.S. Pat. Nos. 4,616,937 and 4,753,535, particular difficulties are experienced when seeking to mix substances of "widely disparate viscosities and/or very different flow rates", because the low viscosity substance tends to "tunnel" through the mixing elements without blending "to any great extent" with the high viscosity substance.
To address the problem, the King '535 patent discloses an apparatus having an outer conduit and an inner conduit, wherein a portion of a flow of a high viscosity substance is converged in a first portion of the inner conduit and passed to a second portion which contains static mixing elements and a port for introducing a lower viscosity substance, the objective being to effect a preliminary mixing of the additive and a portion of the high viscosity substance. The remainder of the high viscosity substance, which passes outside of the inner conduit, and the preliminary mix, which passes from the inner conduit, are directed downstream to a further static mixing device. As also disclosed, the further downstream static mixing device preferably is preceded by a conically shaped element having its apex directed at and substantially aligned with the longitudinal axis of the inner conduit to increase the effective surface area of the premix stream for the downstream static mixing of the preliminary mix and remainder of the high viscosity substance.
On the other hand, the King '937 patent discloses an encased "quill" which is positioned upstream of static mixing devices and which has a discharge port for introducing a low viscosity composition substantially at a centrally disposed position within a tubular conduit through which a higher viscosity composition flows. It further is disclosed that this apparatus preferably has a conically shaped protrusion which precedes the mixing devices and which has its apex directed towards the low viscosity composition discharge port to guide the fluids into a plurality of mixing device ports.
A further known low viscosity additive addition and mixing system, which is manufactured by Komax Systems, Inc., identified as the assignee of the afore-noted King patents, incorporates a device designated as the SIDD injection device. This device is sized to be positioned in a conduit and combined with static mixing disc modules positioned downstream of the device. The injection device includes a plate having a plurality of apertures uniformly sized and uniformly distributed to surround a centrally disposed and protruding cone, wherein each aperture is coincident with the opening of an adjacent downstream static mixing module. The SIDD device is designed to be positioned in a substance flow conduit so that the apex of the cone faces toward the primary high viscosity substance flow and ejects the additives against the flow of the high viscosity substance, the additives being caused by the substance flow to disperse along the outer surface of the cone and pass through the apertured portions of the plate adjacent the cone into the adjacent mixing module.
As the art also reflects, extrusion of plasticizable, or fluidizable, substances long has been practiced with product-exit die devices which are integral with a product discharge end of an extruder means which delivers an extrudate stream to the die devices. Thus, when it is desired to obtain extruded products of differing compositional character, such as may be brought about by, for example, addition of compounds and/or compositions which provide colorant, aromatization, flavorant and/or texturization properties, unless there are a plurality of dedicated extruder lines which employ differing ingredient mixes, an ingredient mix change-over is required. The first case, as will be appreciated, is equipment intensive, and the second is production capacity limiting.
An approach has been suggested in Canadian Patent No. 1 230 005 for producing a co-extruded food product having portions which differ in color, aroma, flavor and/or texture by employing an extrusion device which includes a first conventional screw extruder region, a second region which is partitioned to provide conduits in which extrudate passing from the first region is separated into a plurality of fluxes, i.e., flow streams, and a third convergence region to combine the separate fluxes for forming a composite product. Ports are associated with each separate conduit so that differing additives may be introduced into the separated fluxes to alter such as the color, aromatization and/or texture of the substance of the separate fluxes, and it is disclosed that static mixers may be incorporated into the conduits for effecting mixing of the additives and extrudate prior to recombination of the separated streams in the third region.
Efforts also have been undertaken in the art to split, or partition, the flow of extrudate emanating from an outlet end of a single extruder to facilitate forming an extrudate into a product or to manipulate the extrudate to produce products having differing character. Illustrative of such concepts are, for example, Kamp, U.S. Pat. No. 4,540,537, which discloses a channeled die assembly having a plurality of conduits which terminate in profiled dies for construction of particular plastic closure devices, and Heck, U.S. Pat. No. 4,772,197, which discloses an extrusion die assembly which is particularly useful for producing a plurality of food product strips.
Farnsworth, et al., U.S. Pat. No. 5,110,276, discloses a free-standing extrusion assembly wherein an extrudate from a discharge end of an extruder is partitioned and a plurality of conduits direct the extrudate to die units which enable differing physical manipulation of the product as the product exits the dies of the die units. This arrangement enables production of products which differ such as in shape and provides for, if desired, further extrudate stream partitioning and/or co-extrusion of extrudate streams. Thus, a plurality of products which differ such as in shape and/or composition may be obtained from each die unit. As also disclosed, additives, such as colorants and/or flavorants, may be introduced into one or more of the extrudate flow conduits, after which, each extrudate/additive flow is subjected to mixing, such as with a static mixer, prior to being directed to the die unit.
However, even in view of the afore-noted disclosures, obtaining a substantially homogeneous mixture of substances having differing viscosities without intensive mixing, and without significant in-line pressure loss in the case of static mixing, is still problematical, particularly when the viscosities are significantly disparate and particularly in the case of incorporating additives into certain extrudate products which have been heat-processed, such as is the case, for example, with extrusion-cooking in the food art. Moreover, various additives desired to be incorporated into food extrudates, such as flavorants and aromatics, in particular, are sensitive to heat degradation, and thus, means for effective incorporation of such additives into extrusion-cooked products, other than before or during the extrusion working and cooking, long has been needed and sought to avoid or minimize additive degradation.